twoway: Analysis of Two-Way Tables

Carries out analyses of two-way tables with one observation per cell, together with graphical displays
for an additive fit and
a diagnostic plot for removable 'non-additivity' via a power transformation of the response.
It implements Tukey's Exploratory Data Analysis methods, including a
1-degree-of-freedom test for row*column 'non-additivity', linear in the row and column effects.